The present invention relates generally to automotive transmission shifters and more particularly, to an automotive transmission shifter park lock.
Automotive transmission shifter park locks are known in the prior art. Transmission park locks are devices which disable the transmission shifter once the ignition switch or key is turned to the off position. These devices are intended to prevent the transmission from inadvertently being placed in the neutral position or in gear, for example, by the tampering of a child. Park locks are most often found in vehicles having automatic transmissions.
In the typical prior art automotive automatic transmission park lock, the ignition switch is provided with locking linkage that is interconnected with the transmission shifter by a flexible shielded park lock cable. Flexible shielded cables of this type are known in the art as Bowden cables. The park lock cable is generally connected to the pivotable manually actuated shift lever and is normally displaceable therewith. The ignition switch locking linkage insures that if the transmission is in any position other than the park position, the ignition key cannot be removed from the switch. Most importantly, the ignition switch lock linkage locks the park lock cable in place once the ignition switch is turned off. Since the park lock cable is no longer free to translate with the pivotable shift lever when the ignition is off, the transmission shifter is locked in the park position. In the case of a conventional automotive automatic transmission the vehicle will not roll with the transmission in park and the park lock insures that the automotive transmission cannot accidentally be placed in gear or in the neutral position once the ignition is turned off.
Problems with this type of prior art park lock are related to the fact that all of the park locking forces are generated in the ignition switch linkage. Thus, to transmit these forces to the transmission shifter, a relatively sturdy and expensive park lock cable is required. Furthermore, the ignition switch locking linkage and the park lock cable must be sturdy enough and must be assembled with sufficiently rigorous tolerences to insure that the cable and lock linkage cannot distort and stretch an amount sufficient to allow the transmission to be accidentally placed in gear. Also, since the locking forces are generated in the ignition lock linkage and transmitted via the park lock cable, slack inevitably develops in the linkage and park lock cable from the normal wear of these elements, making it easier to overcome the park lock and creating a potentially dangerous situation.